A water-based composition for post-treatment of metal surfaces

ABSTRACT

A water-based composition for post-treatment of metal surfaces, preferably a silver or silver alloy surface, including:
         an alkanethiol   an anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant with a HLB value of 12 to 18,   a compound of the general formula I:       

     
       
         
         
             
             
         
       
     
     wherein
         R 1  is —H, —CH 3 , —C 2 H 5 , —(C 2 H 4 O) p —H, —(C 2 H 4 O) p —CH 3 , —(C 2 H 4 O) p —CH(CH 3 ) 2 , —(C 2 H 4 ) p —C(CH 3 ) 3 , wherein p is 1 to 20,   R 2  is H, or CH 3      n is an integer in the range of 0 to 3,   m is an integer in the range of 0 to 2.

FIELD OF THE INVENTION

The present invention relates to a water-based composition for post-treatment of metal surfaces, the use thereof and to a method for post-treatment of metal surfaces.

BACKGROUND OF THE INVENTION

Silver and silver alloys are used in electronic devices but it is inevitable that finished articles will require further cleaning and polishing to temporarily remove undesired tarnish products. It is well-known that with exposure to everyday atmospheric conditions, silver and silver alloys develop a lustre-destroying dark film known as tarnish. Prevention of tarnishing of metals and metal alloys is a challenging problem in numerous industries. The tarnishing of metal and metal alloys has been especially problematic in the electronic materials industry where tarnishing may lead to faulty electrical contact between components in electronic devices.

US20070277906A1 discloses for use in treating a metal, e.g. silver or an alloy of silver, a water-based composition comprising a treatment agent selected from an alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide and at least one of an amphoteric, nonionic or cationic surfactant in a concentration that is effective to solubilise the treatment agent.

Preferably the composition comprises at least a non-ionic relatively hydrophobic surfactant e.g. cocamide DEA. The composition is particularly suitable for the treatment of Ag—Cu—Ge alloys.

OBJECTIVES OF THE INVENTION

The objective of the present invention was to provide a composition for effective post-treatment of metal surfaces, particularly silver or silver alloys, in order to prevent tarnishing of such surfaces.

SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION

The invention provides with a water-based composition for post-treatment of metal surfaces, preferably a silver or silver alloy surface, the use thereof and a method. Preferred embodiments are described within the dependent claims.

The metal surfaces are especially surfaces in the field of technical and decorative surfaces either on metal substrates or plastic materials, e.g. on connectors or IC/lead frame applications as well as surfaces on automotive, aerospace, construction, communication, furniture, sanitary and consumer goods.

The invention in particularly provides with a water-based composition for post-treatment of metal surfaces, preferably a silver or silver alloy surface comprising:

an alkanethiol, an anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant with a HLB value of 12 to 18, preferably 15, wherein the water-based composition further contains a compound of the general formula I:

wherein R₁ is —H, —CH₃, —C₂H₅, —(C₂H₄O)_(p)—H, —(C₂H₄O)_(p)—CH₃, —(C₂H₄O)_(p)—CH(CH₃)₂, —(C₂H₄O)_(p)—C(CH₃)₃, wherein p is an integer in the range of 1 to 20, preferably 1 to 10, more preferably 2 to 6, R2 is H or CH₃, preferably CH₃, n is an integer in the range of 0 to 3, preferably 1 to 3, even more preferably 1 or 2, m is an integer in the range of 0, 1 or 2, preferably 0.

HLB values were determined according to the method of W. C. Griffin.

With the present invention, in general or one of the following further embodiments, one or more of the following benefits are obtained:

-   -   enhancing of anti-tarnish properties (particularly proven by K₂S         test)     -   transparent protective coating provides a highly hydrophobic         surface property     -   repelling oxidation agents     -   transparent composition, prevention of negative effects on         appearance of a surface treated with the composition     -   enhanced formation of a self-assembled thiol monolayer onto         immersed silver surfaces, thereby providing with a non-polar         film     -   improved rinsing capability of hydrophobic alkanethiol rests         after silver surfaces treatment, effective elimination of oily         residues

The composition can be an emulsion.

The alkanethiol forms a self-assembled thiol monolayer onto immersed silver surfaces which prevents or retards tarnishing.

The compound of formula I is also called a “gemini surfactant” which has the more general, following structure:

Gemini surfactants are composed of two polar heads (hydrophilic groups) flanked by a spacer to which hydrophobic tails are linked; the spacer can be rigid or flexible, polar or apolar. The invention also discloses using such general surfactants in a composition for post-treatment of metal surfaces. It has been shown that by addition of a surfactant with above structure, particularly by addition of a component of formula I, improved anti tarnishing properties of the composition can be reached.

In a preferred embodiment of the compound of formula I is m=0, n in the range of 0 to 3, preferably n in the range of 1 to 3, more preferably n is 1 or 2, and R₁ is independently selected from the group consisting of R₁ is —H, —CH₃, —C₂H₅ and —(C₂H₄O)_(p)—H with p in the range 2 to 6.

More preferred the compound of formula I is selected from the group consisting of 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 2,2′-[(2,4,7,9-tetramethyl-5-decyne-4,7-diyl) bis(oxy)] diethanol, and 2,4,7,9-tetramethyl-5-decyne-4,7-diolbispolyoxyethylene-ether.

The anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant may have a hydrophobic tail that may linear or branched.

The anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant may be an ethoxylated or propoxylated alkyl, ethoxylated or propoxylated amine, ethoxylated or propoxylated amide, ethoxylated or propoxylated alcohol, or a mixture thereof. A beneficial surfactant is 3-ethoxy-2-methylnonane.

The surfactant may have the general formula II:

R₃O(CH₂CH₂O)_(x)H   formula II

wherein R3 is a linear or branched alkyl group, having 6-15 carbon atoms, preferably 8-12 carbon atoms, x is an integer in the range of 3-15, preferably 7-11.

Preferably the surfactant is a polyethylene glycol, more preferably PEG-11 C10-11 Oxo alcohol ethoxylate (CAS Nr: 78330-20-8).

The water-based composition may comprise a co-emulsifier, which can also be called a “second surfactant”.

The co-emulsifier may have the general formula III

R₄O(CH₂CH₂O)_(y)H   formula III

wherein R4 is a linear or branched alkyl group, having 16-20 carbon atoms, preferably 16-18 carbon atoms, y is an integer in the range of 2-10, preferably 3-6.

The co-emulsifier is preferably polyalkylene glycol ether. Preferably the co-emulsifier is an Alcohol C16-18 ethoxylated propoxylated, (CAS Nr. 68002-96-0).

The alkanethiol is preferably a branched or unbranched C₁₀ - to C₂₀-alkanethiol, more preferred unbranched C₁₀- to C₂₀-alkanethiol, e.g. decanethiol, undecanethiol, dodecanethiol, hexadecanethiol, heptadecanethiol, octadecanethiol, nonadecanethiol, eicosanethiol, most preferably heptadecanethiol, octadecanethiol, nonadecanethiol, eicosanethiol. In one preferred embodiment alkanethiol is octadecanethiol.

In a preferred embodiment, the water-based composition is free of chromate and/or free of organic solvent.

The water-based composition may have a pH in the range of 1 to 6, preferably 2 to 4. The pH may be adjusted by a buffer system. Suitable buffer systems are citric acid/citrate, acetic acid/acetate, tartaric acid/tartrate, phosphoric acid/phosphate or any suitable acid and salts combinations.

The water-based composition may comprise the mentioned constituents in following amounts:

alkanethiol: 0.1-5 g/L, preferably 0.5-4 g/L surfactant: 2-30 g/L, preferably 5-20 g/L compound of formula I: 1-10 g/L, preferably 1-5 g/L; and optionally Co-emulsifier: 0.1-5 g/L, preferably 0.5-2 g/L

In another aspect, the invention is directed to the use of the water-based composition above for post-treatment of metal surface, particularly a silver or silver alloy surface, to avoid tarnishing after metal deposition, particularly after silver or silver alloy deposition.

In still another aspect, the invention is directed to a method for post-treatment of a metal surface, particularly a silver or silver alloy surface comprising, in this order, the steps:

a. providing a metal surface, particularly a silver or silver alloy surface, b. contacting the metal surface, particularly the silver or silver alloy surface, with the water-based composition as described before. Any of the water-based compositions that were described before can be employed.

Contacting can be done by any suitable method. The contacting in step b. may particularly be done by immersing into the water-based composition and/or by spraying with the water-based-composition onto the surface.

Contacting in step b. may be done additionally under electroless conditions, i.e. without supplying a current between the metal surface and an electrode.

In another embodiment, contacting in step b. takes place under applying an electrical current between the metal surface, particularly the silver or silver alloy surface, and at least one electrode when the metal surface is immersed into the water-based composition. The metal surface can act as cathode and the other electrode (which is the counter electrode) can act as anode, or vice versa. Preferably the metal surface is cathodic.

The present invention works preferably with a composition temperature in a range of room temperature (22±2° C.) or higher, more preferably 30° C. or higher, most preferably in a range of 35-65° C.

EXAMPLES

Hereinafter, the invention is illustrated by working examples.

Inventive Example 1

Water-based compositions were provided, wherein the concentrations of c.) compound of the general formula I (compound c1)), vary while the concentrations of other components are fixed, respectively.

The water-based composition was made by dissolving the following components in water:

-   -   a. alkanethiol: octadecanethiol. (CAS Nr. 2885-00-9) amount: 2.5         g/L     -   b. surfactant: PEG-11 C10-11 Oxo alcohol ethoxylates (CAS Nr:         78330-20-8) amount: 17.5 g/l     -   c. compound of the general formula I: c1)         2,5,8,11-Tetramethyl-6-dodecyn-5,8-diol ethoxylate, (CAS Nr.         169117-72-0) in an amount: 2, 3 or 4 g/l     -   d. co-emulsifier: Alcohol C16-18 polyalkylene glycol ether, (CAS         Nr. 68002-96-0) amount: 2,5 g/L.

Inventive Example 2

Water-based composition was provided wherein the following compound c2) 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate (CAS Nr. 9014-85-1) and c3) 2,4,7, 9-tetramethyl-5-decyne-4,7-diol (CAS Nr. 126-86-3) of c.) compound of the general formula I were separately used at same concentrations:

The water-based composition was made by dissolving the following components in water:

-   -   a. alkanethiol: octadecanethiol. (CAS Nr. 2885-00-9) amount: 2.5         g/L     -   b. surfactant: PEG-11 C10-11 Oxo alcohol ethoxylates (CAS Nr:         78330-20-8) amount: 17.5 g/l     -   c. compound of the general formula I (c2 or c3): amount: 2 g/l     -   d. co-emulsifier: Alcohol C16-18 polyalkylene glycol ether, (CAS         Nr. 68002-96-0) amount: 2.5 g/L.

Comparative Example

Comparative water-based compositions were provided, comprising a., b. and d. wherein the concentrations of compound of the general formula I (c1-c3) was zero and the other concentrations were as stated above.

1. Methods

The post-treatment was performed on silver plated copper panels. These panels, having a copper surface, may be provided from the following steps:

-   -   Providing Copper Panels         -   1. Degrease Uniclean™ 260 (electrophoretic alkaline cleaner)             cathodic 7V/45° C./30 sec         -   2. Activate: Uniclean™ 675 (mild acidic             activator)immersion/RT/30 sec         -   3. Pre-silver Pre-silver (low silver concentrated solution)             cathodic 3V/RT/15 sec         -   4. Silver Silverlume Plus (bright silver deposition             solution) cathodic 1 ASD/RT/5 min             -   or AgO-56 (technical silver deposition solution)                 cathodic 1 ASD/RT/5 min             -   or Argalux™ NC mod. (cyanide-free bright silver                 deposition solution) cathodic 0.8 ASD/RT/5 min                 wherein RT is room temperature between 22±2° C.; DI                 water is deionized water; ASD is Ampere per square                 decimeter A/dm² and V is volt/voltage.

In the sense of this invention the post-treatment composition may work also with otherwise obtained silver plated surfaces in the field of use of technical or decorative (with or without cyanide) silver deposition solutions for silver plating to avoid tarnishing after this silver plating.

The inventive water-based compositions according to the invention for post-treatment and the comparative water-based compositions were used under various conditions (see tests below).

After post-treatment in the water-based composition all samples were rinsed with:

-   -   Hot DI water rinse,     -   Cold DI water rinse and     -   dried with compressed air.         -   Optical evaluation after post-treatment with the inventive             and comparative composition and subsequent sulphide test due             to:             -   Residues immediately after post-treatment and rinse             -   Colorations and tarnishing after sulphide test

The observations have been carried out without any instruments by skilled person.

-   -   Sulphide test         -   Material: Glass beaker         -   Chemicals: Potassium Sulphide 44% K₂S, 2% w/w in water         -   Temperature: 22 ±2° C.         -   Dipping time: 5-10 min         -   Evaluation by the skilled person         -   according to colour intensity

2. Results 2.1 Rinsing Capability Test

The inventive water-based compositions showed improved rinsing capability in comparison with the comparative water-based compositions and eliminate oily residues issues completely. The treatment of Silverlume® Plus, AgO-56 and Argalux™ NC mod. plated silver surfaces with the comparative water-based compositions the surfaces showed poor rinsing capability, whereas the inventive water-based compositions show very good rinsing capability.

2.2 Anti Tarnishing Tests

The inventive water-based compositions showed improved anti-tarnish protection in comparison with the comparative water-based compositions without the compound of the general formula I (c1-c3). The not-treated silver surfaces obtained from silver plating solutions as Silverlume® Plus, AgO-56 and Argalux™ NC mod. exhibit very poor anti-tarnish protection. These plated silver surfaces treated with the comparative water-based compositions showed less discoloration after sulphide test, whereas the surfaces treated with the inventive water-based compositions show few to no discoloration.

Test material: bright silver plated surface (Silverlume® Plus)

Water-based composition conditions: pH 2.5—Temperature 55° C.—agitation 200 RPM—immersion process for 1 min, rinse & dry.

Test material: bright decorative silver layer (Silverlume ® Plus) Compound of 0 g/L 2 g/L 3 g/L 4 g/L formula I (comparative (c1-c3) (c1) (c1) example) Residues Very poor Excellent Excellent Excellent (many (none) (none) (none) residues) Anti-tarnish Very poor Improved Strongly Excellent (after 5 min into (dark (yellow improved (no discoloration) K₂S 2%) discoloration) discoloration) (Yellow to no discoloration)

Test material: bright silver plated surface (Argalux NC™ mod), cyanide free

Water-based composition conditions: pH 2.5—Temperature 55° C.—Agitation 200 RPM—1 min immersion process, rinse & dry.

Test material: bright silver cyanide free (Argalux NC ™ mod.) Compound (c1) 0 g/L 3 g/L 4 g/L of formula I (comparative example) Residues Poor (many) Excellent (none) Excellent (none) Anti-tarnish Very poor Strongly improved Excellent (no (after 5 min (dark colored) (yellow colored) discoloration) into K₂S 2%)

Test material: technical silver plated surface (AgO-56™)

Water-based composition conditions: pH 2.5—Temperature 55° C.—agitation 200 RPM—immersion process for 1 min, rinse & dry.

Test material: technical silver (AgO-56 ™) Compound (c1) 0 g/L 3 g/L 4 g/L of formula I (comparative example) Residues Poor (many) Excellent (none) Excellent (none) Anti-tarnish Very poor Strongly improved Excellent (no (after 5 min (dark colored) (yellow to no discoloration) into K₂S 2%) discoloration)

2.3 Cathodic Use

Test material: technical silver plated surface (AgO-56™)

Water-based composition conditions: pH 2.5—Temperature 55° C.—Agitation 200 RPM—immersion for 1 min or cathodic 0.5 A/dm² for 1 min, rinse & dry

Test material: technical silver (AgO-56 ™) Compound 0 g/L 3 g/L (c1) of (comparative example) formula I Process Immersion Cathodic Immersion Cathodic Residues Poor (many) Poor (many) Excellent (none) Excellent (none) Anti-tarnish 5 min 10 min 5 min 10 min (dipping time Very poor Strongly Good (yellow to no Excellent (no into K₂S 2%) (dark colored) improved discoloration) discoloration)

3. Conclusions

-   -   The inventive water-based compositions do improve:         -   The wettability of immersed metal surfaces, especially             silver.         -   The formation of a self-assembled thiol monolayer onto             immersed silver surfaces, making a non-polar film and             enhancing anti-tarnish properties.         -   The rinsing of hydrophobic alkanethiol rests after silver             surfaces treatment with water based solution of the             invention.     -   Immersion and electrophoretic uses are suitable in avoiding         tarnishing of the metal plated surfaces after metal plating. 

1. A water-based composition for post-treatment of metal surfaces, comprising an alkanethiol, an anionic, cationic, non-ionic, amphoteric or zwitterionic surfactant with a HLB value of 12 to 18, characterized in that the water-based composition further contains a compound of the general formula I:

wherein R₁ is —H, —CH₃, —C2H₅, —(C₂H₄O)_(p)—H, —(C₂H₄O)_(p)—CH₃, -(C₂H₄O)_(p)—CH(CH₃)₂, —(C₂H₄O)_(p)—C(CH₃)₃, wherein p is an integer in the range of 1 to 20, R2 is H or CH₃, n is an integer in the range of 0 to 3, m is an integer in the range of 0, 1 or
 2. 2. The water-based composition according to claim 1, wherein in the compound of formula I is m=0, n in the range of 0 to 3 and R1 is independently selected from the group consisting of —H, —CH₃, —C₂H₅ and —(C₂H₄O)_(p)—H wherein p in the range 2 to
 6. 3. The water-based composition according to claim 1, wherein the compound of formula I is selected from the group consisting of 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate, 2,4,7,9-tetramethyl-5-decyne-4,7-diol-bispolyoxyethyleneether, and 2,4,7,9-tetramethyl-5-decyne-4,7-diol.
 4. The water-based composition according to claim 1, wherein the surfactant is an ethoxylated or propoxylated alkyl, ethoxylated or propoxylated amine, ethoxylated or propoxylated amide, ethoxylated or propoxylated alcohol, or a mixture thereof.
 5. The water-based composition according to claim 1, wherein the surfactant has the general formula II R₃O(CH₂CH₂O)_(x)H   (II) wherein R₃ is a linear or branched alkyl group, having 6-15 carbon atoms, x is an integer in the range of 3-15.
 6. The water-based composition according to claim 1, wherein the alkanethiol is a C₁₀- to C₂₀-alkanethiol.
 7. The water-based composition according to claim 1, wherein the composition comprises a co-emulsifier.
 8. The water-based composition according to claim 7, wherein the co-emulsifier has the general formula III R₄O(CH₂CH₂O)_(y)H   (III) wherein R4 is a linear or branched alkyl group, having 16-20 carbon atoms, y is an integer in the range of 2-10.
 9. The water-based composition according to claim 7, wherein the co-emulsifier is a polyalkylene glycol ether.
 10. The water-based composition according to claim 1, wherein the composition is free of chromate and/or free of organic solvent.
 11. The water-based composition according to claim 1, having wherein the composition has a pH in the range of 1 to
 10. 12. (canceled)
 13. A method for post-treatment of a metal surface, in this order, the steps a. providing a metal surface, b. contacting the metal surface, with a water-based composition according to claim
 1. 14. The method according to claim 13, wherein the contacting in step b. is applied by immersing, by spraying, or by any other suitable method, or combination of any of the foregoing, allowing the contact between the metal and the water-based composition.
 15. The method according to claim 13, wherein the contacting in step b. takes place under applying an electrical current between the metal surface, and at least one electrode when the metal is immersed into the claim solution.
 16. The water-based composition according to claim 1, wherein the metal surface is a silver or silver alloy surface. 